1.. Field of the Invention
The present invention relates to a riding work vehicle that includes a vehicle body having a driver's seat; a driving wheel unit supporting the vehicle body; a work unit having a work device that performs work to a worked object around the vehicle body corresponding to running of the vehicle body; and a working electric motor that drives the work device.
2.. Description of Related Art
One of such riding work vehicles described above is a riding electric mower having a mower unit to mow the lawn grass as the work unit. Riding electric mowers have a hybrid vehicle type in which an electric motor supplies rotation power to right and left driving rear wheels and supplies rotation power to a mowing blade of the mower unit, and a battery as an electric source of the electric motor is charged by an engine. Riding electric mowers also have an electric vehicle type that has no engine.
The hybrid vehicle type riding electric mower is described in Related Art 1, for example. The riding electric mower described in Related Art 1 has an electric motor in which right and left driving rear wheels are independently driven and controlled, and smooth turn is achieved by causing the rotation speed of the right and left driving rear wheels to be different from each other. In such a riding electric mower, there is no detailed description of rotation control of the mowing blade.
The electric vehicle type riding electric mower is described in Related Art 2 The riding electric mower described in Related Art 2 uses an electric motor as a driving source of right and left rear wheels that are main driving wheels; a running driving source and a steering driving source of right and left front caster wheels; and a driving source of a mowing blade that is a mowing rotation tool constructing a mower. In this riding electric mower, however, there is no detailed description of rotation control of the mowing blade.
A walking-type battery-powered electric mower operated by a person while walking is designed to efficiently utilize electric power so as to perform mowing work for a long period of time because the battery is small and the capacity is small. In such an electric mower, described in Related Art 3 for example, a battery is connected to a direct-current electric motor in which a mowing edge is attached to an output shaft, and a control unit increasing and decreasing supply current to the electric motor depending on increase and decrease of load is connected between the electric motor and the battery, so as to maintain the rotation number of the electric motor to be substantially uniform at a minimum rotation number or a rotation number close to the minimum rotation number which enables a normal operation of the mowing edge even at heavy load. This control unit reduces power consumption of the electric motor at heavy load to be a minimum necessary for mowing; reduces power consumption more than necessary by curbing the rise of the rotation number of the electric motor at low load; and reduces change in the power consumption with respect to change in the load. That is, control is performed to make the rotation speed of the electric motor uniform as much as possible irrespective of the change in the load. The riding mower, however, performs mowing work in a broad area while running at a much higher speed than a walking speed by using a motor or an engine, and the work load frequently changes depending on the running speed, the lawn density, and the like. Also, taking the directional property of the work into consideration, that is, taking the directional property of the mowing into consideration, there is quite a lot of cases where work running with mowing and non-work running without mowing are repeated in the mowing work. Accordingly, control to make the rotation speed of the electric motor uniform as much as possible cannot effectively save the power consumption.    [Related Art 1] Japanese Patent Laid-Open Publication No. 2009-255840 (paragraphs [0027-0089]; FIG. 3)    [Related Art 2] Japanese Patent Laid-Open Publication No. 2010-184636 (paragraphs [0036-0117]; FIG. 10)    [Related Art 3] Japanese Patent Laid-Open Publication No. H09-201126 (paragraphs [0006-0036]; FIG. 5)